The Command Hub is essentially a Raspberry Pi 3 in a case set up to make using Marty, or Martys easier. You’ll need a USB power source like a phone charger with a USB Micro B connector on one end (the one used for most Android phones). Plug it into the Pi and it’ll start automagically™
There’s also a handy PDF Guide for using the Hotspot.
Please note that the supplied Mains to USB charger has UK type and EU type connectors only, those in the USA, Australia/NZ, China or the rest of the world will need an adaptor or may use another USB power source at their own risk.